linux-kernel - [PATCH] arm64: proton-pack: Fix hard lockup when !MITIGATE_SPECTRE_BRANCH

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Message-ID: <20251117051211.16108-1-jonathan@marek.ca>
Date: Mon, 17 Nov 2025 00:12:08 -0500
From: Jonathan Marek <jonathan@...ek.ca>
To: linux-arm-kernel@...ts.infradead.org
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	James Morse <james.morse@....com>,
	Douglas Anderson <dianders@...omium.org>,
	Trilok Soni <quic_tsoni@...cinc.com>,
	shechenglong <shechenglong@...sion.com>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	Shameer Kolothum <skolothumtho@...dia.com>,
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] arm64: proton-pack: Fix hard lockup when !MITIGATE_SPECTRE_BRANCH_HISTORY

The "drop print" commit removed the whole branch and not just the print.
For some ARM64 cpus, this leads to hard lockup when
CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY is not enabled.

Fixes: 62e72463ca71 ("arm64: proton-pack: Drop print when !CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY")
---
 arch/arm64/kernel/proton-pack.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index c7d70d04c164c..80a580e019c50 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -1032,6 +1032,8 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
 
 	if (arm64_get_spectre_v2_state() == SPECTRE_VULNERABLE) {
 		/* No point mitigating Spectre-BHB alone. */
+	} else if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY)) {
+		/* Do nothing */
 	} else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
 		state = SPECTRE_MITIGATED;
 		set_bit(BHB_HW, &system_bhb_mitigations);
-- 
2.51.0